So I recently purchased some stem cuttings to grow in my tank. I have pebble gravel in there and I placed root tabs under each plant. I have Flourish fertilizer and liquid CO2 that I dose twice a week. My light is on for 10 hours because it’s a florescent light. I’ve noticed the part of the stem in the gravel is just rotting instead of growing roots. Why is this and can anyone help me?